The present invention relates generally to devices for fastening fractured bones. More particularly, this invention relates to an improved bone screw which facilitates minimizing protrusion of the head from the surface of the bone into which the screw is affixed.
It is standard orthopedic procedure to reduce a fracture and secure the reduction with a fastening device inserted into the bone to join the fractured bones. Bone screws are customarily used to reduce the fracture and maintain the fractured bone pieces in physiologically normal alignment during the subsequent healing process. A number of bone fixation devices are known in the art.
Specifically, U.S. Pat. No. 2,489,870 to Dzus discloses a bone fastening device consisting of a lag screw, i.e., a screw having a threaded end portion and a smooth shaft portion, a stud which screwably engages the lag screw and a retaining clip, which is engaged by the stud and tensioned against a bone by action between the lag screw and the stud. The Dzus fastening device is especially useful in correcting spreading of adjacent bones, such as spread mortise of the ankle bones.
U.S. Pat. No. 4,041,939 to Hall, discloses a surgical implant spinal screw which is characterized by a head member having lateral bores for receiving an alignment pin to maintain intervertebral alignment for correction of scoliosis.
U.S. Pat. No. 4,711,232 to Fischer et al discloses a bone fastener consisting of a surgical screw and sleeve. The surgical screw has a head portion having a generally radial symmetry relative to the central axis of the screw. The surgical bone screw of the Fischer et al patent is representative of bone screws widely employed in reducing fracture of small bones, such as the metacarpals and metatarsals.
U.S. Pat. No. 4,569,338 issued to Edwards discloses a sacral fixation screw which has a head member having a laterally oriented slot passing entirely through the lateral aspects of the head. The slot permits engagement of a sacral rod and hook to facilitate longitudinal adjustment of the sacroiliac joint.
Finally, U.S. Pat. No. 4,827,917 to Brumfield discloses a femoral fracture device consisting of a screw and an intramedullary rod. The screw is a lag screw having a head member which has generally radial symmetry relative to a central axis of the screw.
It has been found that the surgical screws typified by the Brumfield and Dzus patents, i.e., those having screw heads with radial symmetry relative to the central axis of the screw, are not ideally well-suited to use in reducing fractures of the bones in the hands or feet. Fractures occurring in the hand or foot, typically involving the metacarpal and metatarsal bones, respectively, present difficulty in reduction due to the narrow diameter of the bone. Moreover, because these bones have closely associated tendons, muscles and ligaments, the protrusion of the screw head above the surface of the bone often causes inflammation of the associated tissues. The resulting inflammation presents a debilitating environment which is not conducive to healing of the bone.
Accordingly, there is a need for a modified surgical screw having modified head configured to minimize protrusion above the surface of the bone.